The teichuronic acid of the cell walls of Micrococcus lysodeikticus is synthesized in vitro by a particulate enzyme fraction which utilizes uridine diphosphate N-acetyl-glucosamine, UDP-N-acetylmannosaminuronic acid and UDP-glucose. The synthesis occurs in two stages and involves several intermediates. Present research effort is directed primarily toward the characterization of these intermediates which are amphipathic and in many respects resemble the undecaprenyl intermediates of peptidoglycan synthesis.